1. Field of the invention
The present invention relates to a solution for cleaning silicon semiconductors and silicon oxides.
2. Description of the Related Art
In the course of production of semiconductor devices, semiconductor wafers and glass wafers are produced, cleaning steps are conducted before various stages.
The cleaning of those wafers, for example, silicon wafers, is performed by a so-called SC-1 cleaning process using primarily a mixture of an aqueous solution of hydrogen peroxide/ammonia water/pure water to remove organic materials and deposited fine particles.
However, such cleaning solution may inevitably cause contamination with Fe, Zn and Al which are trace metal contaminants in the solution. For this reason, all the wafers, from which metal contaminants must be removed, are cleaned by the SC-1 cleaning process, followed by cleaning with acidic solution.
Acidic solution for cleaning may advantageously remove metal contaminants on the surfaces of wafers, but disadvantageously cause adhesion of fine particles contained in the solution onto the wafers in the course of cleaning. Therefore, there has been sought in the semiconductor device and silicon wafer industry a technique capable of cleaning wafers having less contamination with fine particles, if any. Similar circumstances have been prevailing in the field of techniques for cleaning silicon oxides such as quartz glass wafers.
There have been known conventional practical methods related to the cleaning with various acids such as (1) an acidic solution solution containing hydrofluoric acid, sulfuric acid and hydrogen peroxide in water as disclosed in Japanese Patent KOKAI (Laid-open) No. Sho 58-30135, (2) a combination of a mixture of ammonia and hydrogen peroxide in water with a mixture of hydrochloric acid and hydrogen peroxide in water as disclosed in Japanese Patent KOKAI No. Hei 2-100320, (3) an acidic solution containing hydrochloric acid and hydrogen peroxide as disclosed in Japanese Patent KOKAI No. Hei 3-273629, (4) a combination of the cleaning with an aqueous solution of hydrofluoric acid, followed by treatment with hydrogen peroxide as disclosed in Japanese Patent KOKAI No. Hei 4-177725, (5) a solution of strong acid and a very small amount of a compound containing fluorine as disclosed in Japanese Patent KOKAI No. Hei 4-234118, and (6) a solution containing 0.5% hydrofluoric acid and 0.1 to 1% hydrogen peroxide, with which cleaning is conducted at room temperature, as disclosed in, for example, "TRYBOROZIST" Vol. 37, No. 3, (1992) pp. 218-224.
The cleaning solution of the above items (1), (5) and (6) may appear at first sight identical to, but it is definitely different from the solution of the present invention.
The cleaning solution of the above item (1) is for performing degreasing treatment, heavy metals-removing treatment and etching treatment (for removal of residual stress in a ground layer) at the same time, but not for the purpose of inhibiting the adhesion of fine particles during cleaning, which is different in object and industrial utilization from the cleaning solution of the present invention.
The etching depth with the cleaning solution of the invention (1) is of the order of micrometers as shown in Figure accompanied with its specification, while the etching depth achieved by using the cleaning solution of the present invention is of the order of Angstroms.
For example, Examples 22 and 23 shown in Table 1 in the present specification were evaluated for the etching speed to result in about 0.35 Angstrom/min.
The invention (1) does not describe in claims about the composition of the cleaning solution, but refers to a "proportion of HF to be mixed" in the range of about 1.5% or less in its specification, and shows in Figure that "the depth of etching semiconductor wafers" becomes zero in the vicinity of a proportion of HF to be mixed of 0.1%.
It is considered from the foregoing that the "proportion of HF to be mixed" ranges from 0.1 to 1.5% and that the concentration of hydrofluoric acid is definitely different to an extent of orders of magnitude from that of the cleaning solution of the present invention.
The process of the invention (1) comprises "cleaning with a solution containing hydrofluoric acid, sulfuric acid and hydrogen peroxide in water" according to the disclosure of its specification and the "proportion of HF to be mixed" is 1.5% or less as pointed out above, so that the concentrations of sulfuric acid and/or hydrogen peroxide in the cleaning solution must be extremely high. Therefore, the cleaning solution of the invention (1) is different in this point from that of the present invention.
The cleaning solution of the invention (5) comprises primarily a concentrated acid and Table 1 in Example shows typical compositions of cleaning solution where the concentration of sulfuric acid is 88.9% by weight in all cases.
In contrast, the cleaning solution of the present invention comprises primarily water as can be seen from claims and Examples.
The method of the invention (5) describes in paragraph 11 of the specification that a key point of the invention lies in no oxide film observed on the surfaces of the cleaned wafers, which surfaces have been made chemophobic, and in fact all the surfaces of cleaned wafers shown in Table 2 of Example of the invention (5) were made chemophobic.
In contrast, the cleaning solution of the present invention does not impair the hydrophilic property of the surfaces even after cleaning. Therefore, the invention (5) is different from the present invention.
The cleaning solution of the invention (6) and that of the present invention are the same in the point of containing hydrofluoric acid and hydrogen peroxide, but different apparently from each other in the concentration of hydrofluoric acid.
As shown in Table 1 of the present specification, Comparative Examples 58 to 60 indicate that when the silicon wafers made previously hydrophilic by the SC-1 cleaning (APM cleaning) are cleaned with the cleaning solution of the invention (6) containing 0.25% to 0.50% hydrogen fluoride+1% hydrogen peroxide and rinsed with pure water, the surfaces are converted to be hydrophobic with an increase in the number of fine particles adhered after cleaning.
Therefore, the cleaning solution of the invention (6) is completely different from that of the present invention.
As described above, there has been sought a technique for cleaning wafers which is capable of removing metal contaminants with minimum adhesion of fine particles in the production of semiconductor devices, semiconductor wafers and glass wafers.
Industrial development tends to require an increasingly severer level of an reduction in the amounts of metal contaminants and adhered particles to be achieved, which target level becomes difficult to achieve by conventional cleaning techniques.